EXEC(3) BSD Library Functions Manual EXEC(3)
NAMEexecl, execle, execlp, execv, execvp, execvP -- execute a file
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS#include<unistd.h>externchar**environ;
intexecl(constchar*path, constchar*arg_, .../*, (char*)_ */);
intexecle(constchar*path, constchar*arg_, .../*, (char*)_, char*constenvp[]*/);
intexeclp(constchar*file, constchar*arg_, .../*, (char*)_ */);
intexecv(constchar*path, char*constargv[]);
intexecvp(constchar*file, char*constargv[]);
intexecvP(constchar*file, constchar*search_path, char*constargv[]);
DESCRIPTION
The exec family of functions replaces the current process image with a new process image. The func-tions functions
tions described in this manual page are front-ends for the function execve(2). (See the manual page
for execve(2) for detailed information about the replacement of the current process.)
The initial argument for these functions is the pathname of a file which is to be executed.
The constchar*arg_ and subsequent ellipses in the execl(), execlp(), and execle() functions can be
thought of as arg_, arg1, ..., argn. Together they describe a list of one or more pointers to null-terminated nullterminated
terminated strings that represent the argument list available to the executed program. The first argu-ment, argument,
ment, by convention, should point to the file name associated with the file being executed. The list
of arguments must be terminated by a NULL pointer.
The execv(), execvp(), and execvP() functions provide an array of pointers to null-terminated strings
that represent the argument list available to the new program. The first argument, by convention,
should point to the file name associated with the file being executed. The array of pointers must be
terminated by a NULL pointer.
The execle() function also specifies the environment of the executed process by following the NULL
pointer that terminates the list of arguments in the argument list or the pointer to the argv array
with an additional argument. This additional argument is an array of pointers to null-terminated
strings and must be terminated by a NULL pointer. The other functions take the environment for the new
process image from the external variable environ in the current process.
Some of these functions have special semantics.
The functions execlp(), execvp(), and execvP() will duplicate the actions of the shell in searching for
an executable file if the specified file name does not contain a slash ``/'' character. For execlp()
and execvp(), search path is the path specified in the environment by ``PATH'' variable. If this vari-able variable
able is not specified, the default path is set according to the _PATH_DEFPATH definition in <paths.h>,
which is set to ``/usr/bin:/bin''. For execvP(), the search path is specified as an argument to the
function. In addition, certain errors are treated specially.
If an error is ambiguous (for simplicity, we shall consider all errors except ENOEXEC as being ambigu-ous ambiguous
ous here, although only the critical error EACCES is really ambiguous), then these functions will act
as if they stat the file to determine whether the file exists and has suitable execute permissions. If
it does, they will return immediately with the global variable errno restored to the value set by
execve(). Otherwise, the search will be continued. If the search completes without performing a suc-cessful successful
cessful execve() or terminating due to an error, these functions will return with the global variable
errno set to EACCES or ENOENT according to whether at least one file with suitable execute permissions
was found.
If the header of a file is not recognized (the attempted execve() returned ENOEXEC), these functions
will execute the shell with the path of the file as its first argument. (If this attempt fails, no
further searching is done.)
RETURNVALUES
If any of the exec() functions returns, an error will have occurred. The return value is -1, and the
global variable errno will be set to indicate the error.
FILES
/bin/sh The shell.
COMPATIBILITY
Historically, the default path for the execlp() and execvp() functions was ``:/bin:/usr/bin''. This
was changed to place the current directory last to enhance system security.
The behavior of execlp() and execvp() when errors occur while attempting to execute the file is not
quite historic practice, and has not traditionally been documented and is not specified by the POSIX
standard.
Traditionally, the functions execlp() and execvp() ignored all errors except for the ones described
above and ETXTBSY, upon which they retried after sleeping for several seconds, and ENOMEM and E2BIG,
upon which they returned. They now return for ETXTBSY, and determine existence and executability more
carefully. In particular, EACCES for inaccessible directories in the path prefix is no longer confused
with EACCES for files with unsuitable execute permissions. In 4.4BSD, they returned upon all errors
except EACCES, ENOENT, ENOEXEC and ETXTBSY. This was inferior to the traditional error handling, since
it breaks the ignoring of errors for path prefixes and only improves the handling of the unusual
ambiguous error EFAULT and the unusual error EIO. The behaviour was changed to match the behaviour of
sh(1).
ERRORS
The execl(), execle(), execlp(), execvp(), and execvP() functions may fail and set errno for any of the
errors specified for the library functions execve(2) and malloc(3).
The execv() function may fail and set errno for any of the errors specified for the library function
execve(2).
SEEALSOsh(1), execve(2), fork(2), ptrace(2), environ(7)STANDARDS
The execl(), execv(), execle(), execlp(), and execvp() functions conform to IEEE Std 1003.1-1988
(``POSIX.1''). The execvP() function first appeared in FreeBSD 5.2.
BSD January 24, 1994 BSD

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